Oxides for Energy Applications

A Solid Oxide Cell (SOC) is an electrochemical device that can directly convert chemical energy into electricity (fuel cell mode) or conversely electricity into chemical energy (electrolyzer mode). Such devices are composed of layers of oxides and operate at very high temperature (between 500ºC and 1000ºC). Understanding what influences the performances of those oxides is as important as looking at the cell in a whole to predict its performances.

SOC
A solid oxide cell is an all solid state electrochemical device that can directly convert chemical energy into electricity or reciprocally. In the fuel cell mode: hydrogen and oxygen gases are fed and electricity is produced. In the electrolysis mode, water and electricity is fed while hydrogen and oxygen gases are formed.

 

The Effects of Stress on the Defect and Electronic Properties of Mixed Ionic Electronic Conductors

The first area of research interest is the oxide itself, specifically the effects of stress on the properties of mixed ionic electronic conductors, used for examples as electrodes. The compositional strain and thermal expansion mismatch between various constituents of the cell can combine and alter the electronic structure as well as the defect chemistry of the oxide. Using a thermodynamic approach, a model linking stress and change in concentrations is set up, then compared to experimental measurements on thin films. Now, real SOC electrodes are porous which impose spatially varying stress fields; this model is expected to give some insight on the preferred oxygen pathways through such structures.

 

Thermodynamics of Oxygen Bubbles nucleating in the Electrolyte of Solid Oxide Electrolysis Cells

Oxygen bubbles nucleating in the electrolyte of solid oxide electrolysis cells under high currents
A solid electrolysis cells splits water into hydrogen and oxygen gas. The applied potential (or current) is responsible for driving the oxygen ions from one side to the other side. As result, a high oxygen potential develops under the oxygen electrode. Under such conditions, bubbles of oxygen gas can nucleate and dramatically degrade the performances of the cell.

The second area of interest is the electrolysis cell as a whole and the consequences of running a current through it. At high currents, such cells have been reported to degrade very quickly. Oxygen bubble formation has been observed in the electrolyte near the oxygen electrode, and seems to be a source of this degradation. The applied current in the presence of charge transfer resistances is responsible for a high oxygen potential under the oxygen electrode. Under such conditions, bubbles of oxygen gas can nucleate. Local equilibrium imposes an extremely high pressure inside the bubble, introducing, in return, a nonuniform stress field in the oxide. In this second aspect of the project, the stake is to derive the thermodynamics of oxygen bubble nucleation in the electrolyte under an applied current to provide insight on the process and to define critical conditions at which such phenomenon takes place.